Mergui Gr
Type Locality and Naming
Karen–Tenasserim Unit - North, Karen–Tenasserim Unit - South (Phuket Terrain), in the northern part of the KTU, north of the head of the Gulf of Moattama, the sedimentary rocks have been frequently said to comprise the ‘Slate Belt’, an informal term sometimes used synonymously with the Mergui Series rocks of that belt, a term later changed to the Mergui Group (United Nations 1978; Myanmar Geosciences Society 2014). [Original Publication: Barber, A. J., Khin Zaw & Crow, M. J. (eds) 2017. Myanmar: Geology, Resources and Tectonics. Geological Society, London, Memoirs, 48, 317-342]
Lithology and Thickness
Claystone. The United Nations (1978) report has a full account of the Mergui Group, based on outcrops over a considerable distance of the ‘Shan Scarps Area’ where they estimate its thickness exceeds 2500 m. They state that the predominant lithologies are pebbly mudstones, pebbly siltstones and pebbly sandstones; individual units are commonly >20 m thick and lack bedding. Clasts are mostly less than 3 cm in diameter and are mostly quartzite or, rarely, limestone. Mitchell et al. (2002, 2004) describes two Fms in the Mergui Group in the area of the Modi Taung gold deposits; Poklokkale Pebbly Wacke Fm and Kogwe Mudstone Fm.
[Figure: Simplified stratigraphic sections to illustrate the contrasting stratigraphy between the Karen–Tenasserim Unit of central Myanmar and the Shan Plateau, part of the Sibuma block of Ridd (2016) (after Michael F. Ridd, 2017)]
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Relationships and Distribution
Lower contact
Conformable with Taungnyo Fm. A Red Sandstone and Conglomerate unit Fm overlie the Mergui Group around Myeik (Mergui) and on islands of the Myeik Archipelago.
Upper contact
It underlies with Moulmein Limestone Fm
Regional extent
This Gr is developed in Myanmar SE and Myanmar SE Peninsula. In Tanintharyi State (Tenasserim) the Mergui Gr is very widespread (Rao 1930) and extends eastwards across the border into Thailand, where it was referred to as the Phuket Gr by Mitchell et al. (1970) and the Kaeng Krachan Fm by Javanaphet (1969).
GeoJSON
Fossils
Bryozoa and brachiopods.
Age
Depositional setting
The United Nations report (1978) describes westwards increase in regional metamorphic grade in the sediments, independent of the thermal metamorphic effects of the granite intrusions.
Additional Information